The present invention relates to a delay compensation device and a delay line component for a radio frequency low distortion power amplifier used in a radio base station of portable phone communication systems and to a manufacturing method of the delay line component.
In a radio base station of potable phone communication system, the final stage of a radio frequency power amplifier is required to simultaneously amplify a number of different radio frequency signals which are amplitude modulated or frequency modulated for communication. In such a high power radio frequency amplifier used in the radio base station, the signals are usually affected by non-linear operation characteristics of used active components like transistors. Once the signals are affected by such non-linear characteristics, third harmonic inter modulation distortion (hereinafter called as xe2x80x9cIMD xe2x80x9d) is caused and unnecessary radiation interference is resulted. To suppress such interference, some linearisation processing is necessary in radio frequency power amplification. To prevent IMD, an amplifier by feed-forward method (hereinafter called as xe2x80x9cFFxe2x80x9d) is used as shown in FIG. 1 (Japanese Unexamined Patent Publication No.6-224650).
In the figure, the reference number 10 is an input terminal of radio frequency signals for amplification, 11 is the first directional coupler connected with the input terminal 10, 12 is a main amplifier connected with the coupling port of the first directional coupler 11, 13 is a first delay compensation device connected with the primary output port of the first directional coupler 11, 14 is a second directional coupler connected with the output of the main amplifier 12, 15 is a third directional coupler connected with the output of the first delay compensation device 13 and with the coupling port of the second directional coupler 14, 16 is an error amplifier connected with the primary output port of the third directional coupler 15, 17 is a second delay compensation device connected with the primary output port of the third directional coupler 14, 18 is a fourth directional coupler connected with the output of second delay compensation device 17 and with the output of the error amplifier 16, and 19 is an output terminal of amplified radio frequency signals connected with the primary output port of the directional coupler 18.
As will be apparent from FIG. 1, an input radio frequency signal via the input terminal 10 is divided into two signals by the first directional coupler 11, and one of the divided signal is amplified by the main amplifier 12 which generates IMD components (distortion signals) resulted from its non-linearity characteristics in addition to the main signals. The other of the divided signal propagates the first delay compensation device 13 which has a similar delay characteristic as the main amplifier 12. By the directional coupler 15, the output of the delay compensation device 13 is inversely added with the signal, which is adjusted by signal level and phase controllers not shown in the FIG. 1, from the coupling port of the directional coupler 14. As a result, the two main signal components are canceled each other, and only IMD component (distortion signals) is left. The IMD component is amplified at the error amplifier 16 up to the level that is needed to cancel the IMD component generated in the main amplifier 12.
The output signal of the main amplifier 12 propagates the second delay compensation device 17 which has a similar delay characteristic as the error amplifier 16. And the output signal of the second delay line device 17 is inversely added with the IMD component from the error amplifier 16 by the fourth directional coupler 18. Consequently, the two components of IMD are canceled each other and only the amplified radio frequency signal via the input terminal 10 is output via the output terminal 19. By this configuration, a radio frequency amplifier system with good distortion characteristics can be built.
However, this kind of FF type amplifier has problems shown below.
(1) The typical requirement of delay time of the delay compensation device for such amplifier is tens of nanoseconds. If a coaxial cable type of delay line is used for the delay compensation device, the delay time of tens of nanoseconds requires a few meters length of the coaxial cable. That results in very large physical size. And definite propagation loss is resulted when small diameter coaxial cable is applied for physical size reduction.
(2) If a filter by combined resonators is applied for the delay compensation device, more than 10 stages of the resonators are required to achieve tens of nanoseconds. This results in large propagation loss, increased work load of assembling and difficulty in parameter adjusting.
(3) If a micro strip line structure is used as shown in Japanese Unexamined Patent Publication No.2-24120, the propagation loss becomes very large because of electromagnetic energy concentration at the side edges of strip line conductor.
(4) In an actual power amplifier system, the main amplifier and the error amplifier have independent and different frequency transfer characteristics. And in order to completely remove IMD components, the frequency transfer characteristics of the two different amplifiers must be adjusted to be matched each other in a certain frequency range. This requires very complicated and careful tests and adjustments of the main amplifier and the error amplifier after the build of the power amplifier system. The work load of manufacturing is remarkably increased.
It is therefore an object of the present invention to solve the problems in the conventional art, and to provide a delay compensation device, a delay line component and manufacturing method of the delay line component that can contribute to realize small propagation loss in a radio frequency and a very small physical bodied device.
Another object of the invention Is to provide a delay compensation device, whereby two frequency transfer characteristics of a main amplifier and an error amplifier can be easily adjusted and matched each other.
The present invention provides a delay line component with coaxial cable structure, including a center conductor, a dielectric which surrounds the center conductor and an outer conductor which is formed outside the dielectric. The dielectric is made of a ceramic dielectric with a large dielectric constant.
In order to get for example 35 nanoseconds of delay time, 10.5 meters length of a line in vacuum environment is needed. An usually widely used coaxial cable uses dielectric insulator with the dielectric constant of ∈r=2-3, and around 7 meters of such cable is necessary for 35 nanoseconds delay. In the present invention, a large dielectric constant ceramic insulator is used for the coaxial cable dielectric material, and consequently the cable length can be greatly reduced. If the used ceramic insulator""s dielectric constant is ∈r=92, the propagation velocity factor expressed by root square of ∈r becomes about 9.6. The necessary length by such coaxial cable for 35 nanoseconds delay is only about 1.1 meters.
It is preferred that the ceramic dielectric in the coaxial cable structure is made of sintered ceramic materials or a dielectric with a resin in which ceramic particles are included.
It is preferred that at least the center conductor is made of a metal conductor with no grain boundary
It is also preferred that the center conductor is formed by a metal conductor melted and sintered in a center hole of the ceramic dielectric, by a pipe-shaped metal conductor inserted and rolled in a center hole of the ceramic dielectric, or by a wire-shaped solid metal conductor inserted into a center hole of the ceramic dielectric.
If the center conductor is formed by a pipe-shaped metal conductor rolled in the center hole of the ceramic dielectric, preferably, this center conductor is formed by a metal conductor which is expanded by static inside pressure or by explosive gaseous pressure and closely contacted to an inner surface of the center hole.
It is very preferred that the ceramic dielectric is formed by a plurality of independent ceramic dielectric blocks with a predetermined axis length. The electromagnetic mode in a coaxial cable is basically TEM (Transverse Electro-Magnetic Mode), and there is no electric and magnetic field component toward the direction of propagation. The ceramic dielectric is not necessary to be consecutive along the direction of wave propagation in a coaxial cable. This permits to link or stack a plurality of short and proper length ceramic dielectric blocks along the direction of coaxial cable.
Each of the ceramic dielectric blocks may be formed by a cylindrical shaped or polygonal tube shaped block with a center hole.
It is preferred that the outer conductor is formed by a metal film sintered on an outer surface of the ceramic dielectric, or by a pipe-shaped metal conductor which covers in contact the outer surface of the ceramic dielectric.
It is also preferred that the ceramic dielectric located in at least one end portion of the delay line component has a dielectric constant which is different from that of the ceramic dielectric located in another portion of the delay line component.
It is also preferred that the ceramic dielectric located in at least one end portion of the delay line component has a ratio of inner/outer diameters which is different from that of the ceramic dielectric located in another portion of the delay line component.
It is also preferred that the ceramic dielectric located in at least one end portion of the delay line component has an outer diameter which is different from that of the ceramic dielectric located in another portion of the delay line component.
It is preferred that a main delay line portion of the delay line component consists of only a straight coaxial cable line, or includes a plurality of straight coaxial cable lines, and a plurality of curved coaxial cable lines which connect the straight coaxial cable lines with each other.
In the latter case, the dielectric of the curved coaxial cable lines is made of a dielectric with ceramic particles mixed in a soft resin, or made of a plurality of independent ceramic dielectric blocks.
Also, the present invention provides a delay compensation device having a coaxial cable type delay line component with a center conductor, a dielectric which surrounds the center conductor and an outer conductor which is formed outside the dielectric, and a band pass filter connected with at least one end portion of the delay line component.
Since at least one end portion of the delay line component is equipped with the band pass filter, the frequency transfer characteristics of each amplifier can be adjusted to be matched each other.
It is very preferred that the band pass filter is designed so that its frequency transfer characteristics is adjustable.
It is also preferred that an input characteristic impedance and an output characteristic impedance are different with each other in the band pass filter. Thus, impedance matching between the delay line component and external circuit connected thereto can be possible.
It is preferred that a band pass filter is connected with only one end portion of the delay line component, or that band pass filters are connected with the both end portions of the delay line component, respectively.
Furthermore, the present invention provides a method of manufacturing a coaxial cable type delay line component which includes a center conductor, a dielectric which surrounds the center conductor, and an outer conductor which is formed outside the dielectric. The method includes a step of forming the dielectric by linking a plurality of linked independent ceramic dielectric blocks with a predetermined axis length by glass paste and by sintering them to make a long integral member.
It is preferred that the dielectric is made of a sintered ceramic dielectric with a large dielectric constant.
Also, the present invention provides a method of manufacturing a coaxial cable type delay line component which includes a center conductor, a dielectric which surrounds the center conductor, and an outer conductor which is formed outside the dielectric. The method includes a step of forming the dielectric by mixing ceramic particles in a resin.
It is preferred that at least the center conductor is made of a metal conductor with no grain boundary.
It is preferred that the center conductor is formed by filling metal material into a center hole of the ceramic dielectric, and by melting and sintering the filled metal material, formed by inserting a pipe-shaped metal conductor into a center hole of the ceramic dielectric, and by expanding the pipe-shaped metal conductor by static inside pressure or explosive gaseous pressure to closely contact to an inside surface of the center hole, or formed by inserting a wire-shaped solid metal conductor into a center hole of the ceramic dielectric.
It is also preferred that the outer conductor is formed by covering an outer surface of the ceramic dielectric with a metal paste and by sintering the metal paste, or formed by covering an outer surface of the ceramic dielectric with a pipe-shaped metal conductor.